It is often desirable to determine whether a secure installation has remained unpenetrated over a given period of time. Mere inspection of the locking mechanism does not provide this information. It is impossible to determine whether the lock has been opened and re-closed or to determine whether the original lock has been destroyed and replaced by an identical substitute lock.
To overcome these problems, it has been a practice to attach a seal to the lock. A seal is a device which is irreparably broken or altered when the original lock is opened. A wide variety of seals are currently available.
Fiber optic seals have been described in U.S. Pat. Nos. 4,106,849; 4,407,415; 4,130,341 and 4,262,284. In each of these devices, a fiber optic bundle is passed through a fastening or locking device. By exposing one end of the bundle to a light source and observing the light emitted from the other end of the bundle, it is possible to determine whether anyone has tampered with the seal.
One problem with the known fiber optic seals is that they are relatively complex and hence are relatively difficult and expensive to produce. A need exists for a low cost seal with high integrity and tamper resistance. The present invention fulfills this need.